Presents for the DS (x3) and DiL

London bus for the DGS? Notepads etc from the National Gallery or the British Museum? T shirt with Cambridge University or other printed on it?
Where are you in the uk? Something local?

I post to USA box of up to 2kg weight. This has bits and pieces from 'over here' that wouldn't be available in the USA. Local shortbread, confectionary, a piece of local craftwork etc. Nice clothing from TK Maxx for dgs age 4. One of the biggest hits was hand knitted aran hats, not heavy. A hand knitted aran jumper for dgs etc. I can no longer knit these myself because of aches and pains but it's easy to find them on eBay where folks knit and sell.

Up to 2kgs posts from the UK to the USA for about £24, supposedly 7 days delivery but in reality it's more like 10 days. When looking for gifts size and weight is everything. In the past I've sent cashmere scarves, a throw which was pure wool and light as a feather and made locally. Also sent a clock made from driftwood, also very lightweight.

I then go to Amazon.com which is the US site and order our main christmas gift for dgs and have it delivered direct to their home address. Delivery is usually free. Gift wrapping is often an option though I don't do it as it's quite expensive.

I sometimes have flowers or a plant delivered as a gift. I googled for a florist in their post code and then telephone them to place the order. Definitely wouldn't use Interflora or any other online florist as have been let down by the quality.

My DS never have much luggage and DS2 is taking a case specifically to transport presents- possible even a bag which he can fold away or leave there to avoid having to bring a case back (Frankfurt airport is a nightmare and you have to walk miles to the baggage reclaim area).

I wish I could give them to him unwrapped, but I'm not sure they would wrap them up. I would not stick them down, of course. We have always taken presents with us with the paper folded separately and wrapped them there.

I forgot to add that I'm looking for ideas for things that can't be bought in the States. No point in getting them anything like that, of course.

They'll be getting money, anyway, at least the two who are travelling over will be, to help with their travel expenses and because they both have November birthdays. But it would be nice for them to have something to unwrap. The DGS is 3 an a half.

You need to think very carefully - this could end up being very time-consuming and potentially costly for your DS

You cannot send wrapped presents as customs will just unwrap them. Your DS may also find that he has to pay customs duties on the gifts. In addition taking a lot of gifts can be heavy and bulky and may significantly increase the weight of his baggage so that he has to pay excess baggage costs as well.

My advice would be to send gift vouchers or perhaps purchase gifts online using a US site or a UK site that ships to the US so they can be wrapped and delivered direct.

Wrapped parcels can pose problems. If you are going to send them presents, don't wrap them - they are likely to be unwrapped in customs anyway. U.S. Customs do NOT like wrapped parcels!
Vouchers are a good idea - they might decide to go out and have a shopping day together, you could throw in money for a meal out for the grown ups. You don't say how old gcs are. Send something for them as a present, but don't wrap, get the mums to do that.

I'd just give them vouchers or even cash. Loads of presents would hold things up at customs.

They will need customs clearance , fancy wrapping or not , are you sure they will be willing and able to add this stash to their luggage allowance ?

Amazon vouchers.